1. Field of the Invention
The present invention is related to an analog-to-digital converting method and related functional device, and more particularly, to an analog-to-digital converting method and related functional device which decompose and convert an analog signal.
2. Description of the Prior Art
With advances in integrated circuit manufacturing, an analog-to-digital converter (ADC) is allowed to output a digital signal composed of more bits. In such a situation, a value represented by the digital signal can more precisely approach an analog signal received by the ADC. To do so, the ADC requires more circuit layout area, complexity, and robustness against noise. If noise rejection of the ADC is insufficient, signal distortion occurs during the analog-to-digital conversion, which offsets advantages of the additional bits of the digital signal.
For example, please refer to FIG. 1, which is a schematic diagram of an audio amplification device 10 of the prior art. The audio amplification device 10 adjusts volume of an audio signal ADO based on a reference voltage VR, and includes an ADC 100 and an amplifier 110. The ADC 100 is utilized for converting the reference voltage VR into an N-bit volume control signal VOL. The amplifier 110 is utilized for adjusting the volume of the audio signal ADO according to the volume control signal VOL to output an adjusted audio signal ADO′.
Please continue to refer to FIG. 2, which is a schematic diagram of a conversion relationship between the reference voltage VR and the volume control signal VOL in the ADC 100. In general, a voltage range of the reference voltage VR is between a power voltage VDD and a ground voltage VGND. If the power voltage is 5V, the ground voltage is 0V and N=6, every stage of the volume control signal VOL corresponds to (5-0)/26=78 mV of the voltage range of the reference voltage VR. That is, the ADC 100 utilizes 78 mV as a unit to convert the reference voltage VR into the volume control signal VOL. If the power voltage VDD decreases from 5V to 2.5V or the bit number N increases from six to seven, the conversion unit of the ADC 100 further decreases to 39 mV. In other words, if the power voltage VDD decreases or the bit number N increases, the ADC 100 requires higher conversion accuracy.
Once the reference voltage VR is given, the corresponding N-bit volume control signal VOL is acquired. However, when the audio amplification device 10 outputs high power, the power voltage VDD and the ground voltage VGND tend to vibrate. In such a situation, stages of the volume control signal VOL vibrate with the power voltage VDD and the ground voltage VGND, and therefore the reference voltage VR is converted into an erroneous volume stage and varies with output. When the stage height is further compressed due to the increased bit number N for more volume stages, probability of erroneous conversion increases, resulting in unstable volume of the audio amplification device 10. In a worse case scenario, when pins of the audio amplification device 10 are insufficient, the ADC 100 and the amplifier 110 have to share power reception pins, and parasitic resistors existing on the shared power reception routes deteriorate the offsets of the power voltage VDD and the ground voltage VGND and enlarge variation of the volume control signal VOL value corresponding to the given reference voltage VR.
Therefore, stabilization of conversion with a precision enhanced ADC has been a major focus of the industry.